The present invention relates to an oxidation gas discharging structure. The discharging structure is applied to a fuel cell stack, which includes an end plate arranged at an end of a fuel cell body and discharges oxidation gas inside the fuel cell body to the outside through a through hole, which extends through the end plate.
This type of fuel cell system includes a fuel cell stack, which includes a fuel cell body formed by stacking a plurality of cells and two end plates holding the fuel cell body from the sides in the stacking direction of the cells. For example, refer to Japanese Laid-Open Patent Publication No. 2011-222203.
A fuel cell stack disclosed in this document includes supply passages, which supply the fuel cell body with fuel gas (e.g., hydrogen), oxidation gas (e.g., air), and coolant, respectively. The fuel cell stack also includes discharge passages, which discharge the fuel gas, the oxidation gas, and the coolant from the fuel cell body, respectively.
A conventional fuel cell system includes a compressor and the like, which are arranged upstream of the oxidation gas supply passage and feed oxidation gas to the fuel cell stack. A first end plate includes a through hole that forms a part of the oxidation gas discharge passage. A connection pipe is connected to the through hole, and a sealing valve is arranged downstream of the connection pipe. The driving of the compressor is controlled to adjust the supply flow rate of oxidation gas and to adjust the open/closed state of the sealing valve, thereby controlling the pressure of oxidation gas that flows inside the fuel cell stack.
When the operation of the fuel cell system is stopped, supply of oxidation gas is stopped. At this time, the ambient air may flow into the interior of the fuel cell body through the oxidation gas discharge passage. When the ambient air flows into the fuel cell body, electrochemical reaction continues with oxygen contained in the ambient air and the fuel gas remaining inside the fuel cell body after the operation is stopped. Thus, in the conventional device, the sealing valve is closed after operation of the fuel cell system is stopped to prevent ambient air from flowing into the interior of the fuel cell body.
For example, when the ambient air temperature decreases below freezing after the operation of the fuel cell system is stopped, the following problems may occur. When the temperature of the fuel cell stack decreases along with the decrease of the ambient air temperature, water vapor that is present in the oxidation gas discharge passage is condensed to become condensed water and moves toward the outside through the discharge passage. However, since the sealing valve is closed after operation stop of the fuel cell system as described above, the condensed water is accumulated in the sealing valve. When the temperature of the condensed water decreases below freezing, the condensed water is frozen and adheres to the sealing valve.